The invention relates to a method for single color dyeing a textile web of fabric by means of a padding machine with a web squeezer. The squeezing force distribution between the rollers of the padding machine is controlled according to the dye distribution in the web of fabric that is still provided with the initial humidity on the output of the padding machine. The dye distribution is measured on certain points by means of a dye measuring appliance.
A method of this type is described in EP 0 411 414 B 1. Through the known dye measurement of the web of fabric, which is still damp, possible deviations of the dye distribution from the target value can be detected practically immediately after leaving the padding machine. Hence only a few meters of web of fabric are needed to regulate the squeezing force distribution of the rollers of the padding machine necessary for the predetermined dye distribution. Readjustment may be permanently made when operating such an installation.
The dye measuring instruments for the implementation of the known method are however, when put into practice, so costly that as a rule only one dye measuring instrument is available for the whole width of a web of fabric, for example 3 meters. The instrument must therefore be moved back and forth on rails laterally to the direction that the web is moving. For cost reasons many users do not employ the environmentally friendly method at all. Added to this is also the disadvantage that when employing the known method, the dye measuring instruments used could only measure the total dye impression.
With regard to dye measuring, it is also known from EP 0 411 414 B1 and DE 42 38 234 A 1 that in addition to a brightness measurement in the visible area, a dampness measurement should also be taken on a textile web and both measuring signals should be used to control the squeezing force distribution of the padding machine squeezers. In the known method two brightness sensors (one for visible, one for infrared light) are even needed at every measuring point. Nevertheless, the instruments can only detect the total brightness impression in each measurement area. When single-color dyeing, pure dyes are practically never used. Mixed dyes are almost always used instead. A dye applied to a web of fabric in a padding machine contains therefore a mixture of dye particles of varying dyeing effect, e.g. red, yellow, and black dye particles in the predetermined mixing ratio.